We address the thermally induced abrupt shrinking of a large-radius donor in a ferromagnetic semiconductor. The sudden and severe localization is viewed as the synergistic effect of the driving forces for localization provided by the thermally induced spin disorder and the tendency for self-trapping. To show this effect, we calculate the free energy of a donor state in a ferromagnetic semiconductor. The donor electron interacts with the atomic spins via an intra-atomic exchange interaction and with the atomic displacements via a short-range electron-lattice interaction. Consistent with our focus on temperatures well below the Curie temperature, the spin deviations are treated within the spin-wave approximation.As a result of the short-range electron-lattice interaction, the free energy can have two distinct minima. One corresponds to a large-radius donor with but a weak interaction with the atomic displacements. The second minimum corresponds to a severely localized donor which has the strong interaction with the atomic displacements characteristic of a small po- laron. With rising temperature the energy of the minimum associated with the severely localized donor state is lowered relative to that of the large-radius donor. Hence, a system in which the large-radius donor is stable at low temperatures may experience an abrupt donor-state collapse as the free-energy minimum associated with the severely localized donor passes below that of the large-radius donor. The problem of the donor-state collapse illustrates what we believe to be a common phenomenon. Namely, with a short-range electron-lattice interaction, an electron will either form a small polaron or it will experience minimal polaronic effects.The state of the system is essentially determined by the ratio of the electron's kinetic energy to the small-polaron binding energy. With a near-equality of these two energies, a modest amount of disorder may provide a sufficiently strong driving force for localization to tip the balance and induce a small-polaronic state. In the present example, the spin-disorder energy is but a fraction of either the electron's kinetic energy or the small-polaron binding energy. While our calculation is not quantitative, numerical estimates provide reasonable estimates of the physical parameters.